1. Field of the Invention
The present invention relates to a rod for a coating device, on the surface of which a coating having abrasion resistance is formed, and a process for producing the same, and more specifically relates to a rod for a coating device which is suitable for coating a body to be coated, such as a continuously-running web, with a coating solution, and a process for producing the same.
2. Description of the Related Art
It is widely performed that, when a photosensitive material, a photoengraving process material, a magnetic recording material, recording paper material, a photosensitive planographic printing plate, or the like is produced, a sheet-form or web-form body to be coated (substrate to be coated) made of a thin metal, paper, film or the like is continuously run in a longitudinal direction and simultaneously one single side thereof is coated with a coating solution (photosensitive solution).
In many cases, at the time of the coating, a rod (bar) for a coating device is brought into contact with a surface of the body to be coated, and the rod is rotated while the coating solution is supplied onto the surface of the rod, whereby the coating is attained. This coating process is called bar coating process.
For example, as illustrated in FIG. 8, in a rod 40 for a coating device (referred to merely as the rod 40 hereinafter) in the prior art, grooves 48 are generally made in the surface along the circumferential direction, and a coating 44 having abrasion resistance is formed on a columnar base material 44 by surface reforming treatment. The formation of the coating 44 can be performed in various manners such as plating, physical vapor deposition and chemical vapor deposition.
A first problem to be solved for a rod for a coating device in the prior art is that in the case that the rod 40 is used to perform high-speed coating (in particular, in the case that high-speed coating is applied to an anodizated aluminum web), convex portions 46 made in the rod 40 are abraded in a short time. In the case that the convex portions 46 are abraded in a short time in this manner, the grooves 40 made in the rod 40 become shallow so that the adjustment precision of the amount of a coating solution with which a body to be coated, such as a web, is coated lowers. As a result, it is necessary that the rod 40 is frequently exchanged. This is a serious problem for attainment of an improvement in productivity and energy-saving in the step of coating the web with the coating solution. Even in a rod for a coating device in which no grooves are formed, its coating is partially abraded so that the same problem is caused.
Examples in which a countermeasure against the problem is taken are disclosed in Japanese Patent Application Laid-Open (JP-A) Nos. 2001-901, 2000-343012, 2000-354808, 2000-334349, and 04-048956.
Incidentally, in order to improve the abrasion resistance of the rod surface, it is effective to take measures considering both of the hardness of the coating 44 and the friction coefficient between the coating 44 and the web (body to be coated) W. However, the above-mentioned publications never describe consideration of the two.
In order to form the abrasion-resistant coating 44, it is preferred to use ion plating. However, no publications disclose which manner of ion plating should be used for the film formation. When the film is formed in a holocathode manner from among ion plating manners, a uniform and good coating is formed over a wide area. Such examples are disclosed in JP-A Nos. 55-100975, 1-240646, 5-25617, and 8-100254. However, the publications never consider that such examples are applied to a rod for a coating device.
A second problem to be solved for any coating device rod in the prior art is that in the case that a large shearing force or normal stress is applied to the surface of the rod when the rod is used, its coating is chipped or peeled from its base material. A main cause for this is that residual stress generated in the coating is large. This residual stress is generated by a thermal expansion difference between the base material and the coating.
The problem is generated not only in coating device rods in which grooves are made in the surface along the circumferential direction but also in coating device rods in which no grooves are made.
Examples in which a countermeasure against this problem is taken are disclosed in JP-A Nos. 2001-901, 2000-343012, 2000-354808, and 2000-334349.
Incidentally, in order to prevent the coating of a coating device rod from being chipped, it is effective to take measures considering both of the film thickness of the coating and a thermal expansion coefficient difference between the coating and the base material. However, these publications never describe consideration of the two.
A third problem to be solved for any coating device rod in the prior art is that at the time of forming a coating thereon, very small cracks (chippings) are generated in the coating. This is based on a large difference in thermal expansion between the base material and the coating. The generation of the chippings is a serious obstruction against an improvement in the productivity of the coating device rod.
The problem is generated not only in coating device rods in which grooves are made in the surface along the circumferential direction but also in coating device rods in which no grooves are made.
Examples in which an intermediate layer is formed, as a countermeasure against the problem, between the base material and the coating are disclosed in JP-A Nos. 6-64087 and 2000-354808.
However, thermal expansion is never taken into consideration in these publications. Thus, it is desired to take further measures.
A fourth problem to be solved for any coating device rod in the prior art is about the process for producing the same. As described above, an abrasion-resistant coating is generally formed on the surface of the coating device rod. The formation of the coating can be performed in various manners such as plating, physical vapor deposition, and chemical vapor deposition. In many cases, however, a vacuum chamber is used to form the coating by physical vapor deposition such as ion plating. From the viewpoint of abrasion resistance, it is preferred to form the coating uniformly. Accordingly, when the coating is formed by ion plating, various means are adopted to form this coating uniformly.
For example, in JP-A No. 63-192855, ionization efficiency is improved to form a uniform coating in a large area. In JP-A Nos. 01-240646 and 01-252764, in order to form a uniform coating in a large area, ionization efficiency is improved and the speed of forming the coating is made high.
However, when a columnar base material, which is a body to be coated, becomes significantly long, an ordinary chamber cannot receive the base material. Even if a large-sized chamber can receive the long base material, a vapor deposition source is then often set up at a position apart from the center of such a large-sized chamber. In other words, due to the restriction by the size of the chamber, the base material cannot be arranged right above the vapor deposition source in many cases. Therefore, there arises a problem that a coating having a large thickness is formed in base material regions near the vapor deposition source, and a coating having a small thickness is formed in base material regions far from the vapor deposition source. Even if the center of the base material can be arranged just above the vapor deposition source, there arises a problem that when the base material is relatively long, the thickness of the formed coating is smaller at both ends of the base material than at the center thereof.
JP-A No. 02-077573 or 02-079764 describes an example in which a long object, which is a body to be coated, is continuously run and simultaneously a coating is uniformly formed by ion plating. However, such an example cannot be applied to the case that a coating is formed on a non-continuous object, such as a base material of a coating device rod.